Multiple cylinder internal combustion engine

ABSTRACT

A multicylinder internal combustion engine is provided with a plurality of cylinders sharing a single crankshaft. The combustion characteristics in the respective cylinders is improved by taking out part of combustion (expansion) gas produced in one of the cylinders at an earlier stage of the explosion (expansion) stroke, and then introducing the gas into another one of the cylinders in the suction or compression stroke.

TECHNICAL FIELD

[0001] The present invention relates to a multicylinder internalcombustion engine including a plurality of cylinders sharing a singlecrankshaft.

BACKGROUND ART AND PROBLEMS TO BE SOLVED BY THE INVENTION

[0002] “Scientific Lecture Meeting Preprints 782”, published in October,Showa 53, by Society of Automotive Engineers of Japan, INC., includes anarticle [45] Combustion Analysis of Gasoline Engines—from the Viewpointof Intermediate Combustion Product-(pages 353-362). This article saysthat burning of gasoline-air mixture starts with the generation ofactive intermediate products or radicals such as CH- and OH-groups, andthen successive burning of the active radicals will follow. Further, itsuggests that the active radicals in mixture of air and hydrocarbon fuelsuch as gasoline can reduce the ignition temperature and ignitionpressure for the mixture, thereby contributing to the improvement incombustion characteristics of the mixture.

[0003] In light of the above, the present invention is proposed toimprove the combustion characteristics of the gas mixture in thecylinders of a multicylinder internal combustion engine that consumes ahydrocarbon fuel such as gasoline, or hydrogen fuel.

[0004] Regarding prior arts which may be relevant to the presentinvention, JP-A-H05-157008 and JP-A-2000-282867 teach that:

[0005] “A pressure accumulation chamber is designed to communicate witha combustion chamber so that part of combustion (expansion) gas duringthe explosion (expansion) stroke is stored in the pressure accumulationchamber, and the stored combustion (expansion) gas is discharged intothe combustion chamber during the suction stroke or the compressionstroke.”

[0006] Further, JP-U-H05-83351, JP-A-H05-187326 and JP-A-H09-68109 teachthat:

[0007] “In a multicylinder internal combustion engine with a pluralityof cylinders sharing a crankshaft, part of combustion (expansion) gas inone cylinder undergoing the explosion (expansion) stroke is introducedinto another cylinder undergoing the suction stroke or the compressionstroke.”

[0008] The radicals, generated in burning gas mixture, increase inamount when the combustion temperature rises, but they are turned intostable substances such as carbon monoxide, hydrogen or methane as thecombustion temperature drops. Thus, their activity is highlytemperature-dependent and degrades with a drop in temperature.

[0009] According to the former group of prior arts mentioned above, partof combustion (expansion) gas in the explosion (expansion) stroke isstored in the pressure accumulation chamber, and the stored gas isdischarged during the suction stroke or the compression stroke. Withthis arrangement, the temperature of the combustion (expansion) gasstored in the pressure accumulation chamber drops greatly as the processproceeds from the explosion (expansion) stroke to the suction stroke orcompression stroke through the discharge stroke. As a result, most ofthe radicals contained in the stored combustion (expansion) gas willdisappear by turning into unexcited products or stable produces (such asCO, HC, H₂ and H₂O) Thus, the former group of prior arts can increasethe compression pressure and decrease NOx by the effect of EGR, butcannot improve the combustion characteristics of gas mixture by radicalsto be generated by combustion.

[0010] The latter group of prior arts mentioned above is merely designedto perform recirculation of exhaust gas into the suction stroke for thepurposes of reducing NOx by the EGR effect. Specifically, part ofexhaust gas is drawn from a cylinder at the substantial end of itsexplosion (expansion) stroke to be introduced into another cylinder.Since the combustion temperature has been dropped considerably by theend of the explosion (expansion) stroke, most of the radicals in thecombustion (expansion) disappear by turning into stable products.Therefore, the introduction of the combustion (expansion) gas intoanother cylinder cannot improve the combustion characteristics of gasmixture in the cylinder.

[0011] The objective of the present invention is to ensure that thecombustion characteristics of gas mixture in the cylinders of amulticylinder internal combustion engine is improved by utilizing theradicals generated by combustion in the cylinders.

DISCLOSURE OF THE INVENTION

[0012] According to a first aspect of the present invention, there isprovided a multicylinder internal combustion engine provided with aplurality of cylinders sharing a single crankshaft. The engine comprisesarrangement for the respective cylinders, whereby part of combustion(expansion) gas is taken out from one of the cylinders at an earlierstage of an explosion (expansion) stroke, and introduced into anothercylinder of the remaining cylinders in a suction stroke or compressionstroke through a communication path.

[0013]FIGS. 9, 10 and 11 illustrate the relationship between the crankangle and the cylinder pressure or the combustion temperature in afour-stroke, three-cylinder internal combustion gasoline engine with atotal displacement of 660 cc, the revolution per minute being 2000, 4000and 6000, respectively.

[0014] As indicated by the solid curve line C in these figures, thecombustion temperature in a cylinder rapidly rises immediately after theignition which occurs at around the top dead center at a crank angle ofsubstantially 0 degree to reach the maximum temperature and rapidlydrops when the exhaust valve is opened at a crank angle of substantially120 degrees. Thus, the combustion temperature is high in an earlierstage in the explosion (expansion) stroke, i.e. the time period from thetop dead center to the time when the crank angle becomes about 120degrees, so that the combustion (expansion) gas produced in this timeperiod contains a large amount of active radicals of a so-called highenergy level.

[0015] Further, as indicated by the dotted curve D, the pressure in thecylinder rapidly rises immediately after the ignition to reach themaximum pressure and then drops. Thus, the pressure is high during thefirst half of the explosion (expansion) stroke.

[0016] With the above-noted arrangement, in which part of combustion(expansion) gas produced in one of the cylinders at an earlier stage ofthe explosion (expansion) stroke is taken out for introduction intoanother cylinder in a suction stroke or a compression stroke, it ispossible to take out part of combustion (expansion) gas which has a hightemperature and hence contains a large amount of active radicals. Then,the extracted part of the combustion (expansion) gas is introduced, viaa communication path, into another cylinder which is in a suction strokeor a compression stroke. As a result, the combustion characteristics ofgas mixture in the cylinders can be reliably and greatly increased bythe radicals produced by the previous combustion of the gas mixture inthe cylinders.

[0017] According to a second aspect of the present invention, acompression ratio in each of the cylinders is set to such a high valueas would lead to abnormal combustion such as knocking during high-loadoperation. The engine further comprises arrangement for the respectivecylinders during the high-load operation, whereby part of combustion(expansion) gas is taken out from one of the cylinders at an earlierstage of an explosion (expansion) stroke, and introduced into anothercylinder of the remaining cylinders in a suction stroke or compressionstroke through a communication path.

[0018] By taking out part of combustion (expansion) gas from one of thecylinders at an earlier state during the explosion (expansion) stroke,the combustion pressure is lowered. Thus, it is possible to preventabnormal combustion such as knocking during high-load operation fromoccurring.

[0019] The combustion (expansion) gas taken out at the earlier stage inthe explosion (expansion) stroke contains a large amount of radicals,which is active and has a high energy level due to the high temperatureof the combustion (expansion) gas. By introducing the taken-outcombustion (expansion) gas into one of the cylinders that is undergoingthe suction or compression stroke, the combustion characteristics in thecylinder can be considerably improved by the radicals contained in thesupplied combustion (expansion) gas. The combustion characteristicsimprovement contributes to the increase in output of power. Thus, it ispossible to compensate for the power reduction due to the partialextraction of the combustion (expansion) gas at the earlier stage of theexplosion (expansion) stroke.

[0020] A high compression ratio may be adopted to increase the mileageand the output during the frequently utilized low- or middle-loadoperation. Even in such a case, abnormal combustion such as knockingduring a high-load operation can be reliably prevented, and no powerreduction occurs.

[0021] According to a third aspect of the present invention, a singlecommon communication path is provided which extends along a row of thecylinders and which is connected to combustion chambers of the cylindersvia communication paths provided for respective cylinders. Each of thecommunication paths is provided with an open/close valve which opens atan earlier stage in an explosion (expansion) stroke of the cylinder forintroducing part of combustion (expansion) gas produced in the cylinderinto another one of the cylinders which is in a suction stroke or acompression stroke.

[0022] With this arrangement, heated combustion (expansion) gasresulting from the combustion (expansion) in any one of the cylinderswill flow back and forth through the single common communication path atshort intervals. Accordingly, the common communication path can beheated to a higher temperature than a communication path that wouldconnect two cylinders to each other but to the others. Thus, thecombustion (expansion) gas taken out from one cylinder does not largelydecrease its temperature in passing through the common communicationpath. The heated combustion gas, containing a large amount of radicals,can be introduced into another cylinder in a suction stroke or acompression stroke. Further, the design of a single common communicationpath for all the cylinders can simplify the forming of communicationmeans among the cylinders.

[0023] According to a fourth aspect of the present invention, a singlecommon communication path is provided which extends along a row of thecylinders and which is connected to combustion chambers of the cylindersvia communication paths provided for the respective cylinders. Each ofthe paths is provided with an open/close valve. Further, each cylinderis provided with an ion current detector for detecting ion current incombustion (expansion) gas during the explosion (expansion) stroke ofthe cylinder so that the open/close valve of the cylinder opens when theion current in one of the cylinders is determined to be high based on adetection signal from the ion current detector, so that part of thecombustion (expansion) gas is introduced into another one of thecylinders in the suction or compression stroke.

[0024] It is known that ion current flows during the combustion of gasmixture in a cylinder, the ion current being generally proportional tothe pressure in the cylinder during the combustion (See JP-A-H06-299942,for example). As seen from FIGS. 9, 10 and 11, the pressure in thecylinder during combustion is generally proportional to the combustiontemperature of gas mixture.

[0025] Keeping the above in mind, ion current detecting means may beprovided in each of the cylinders for detection of ion current incombustion (expansion) gas in the explosion (expansion) stroke. Based ona detection signal from the ion current detecting means, the open/closevalve of the communication path for each cylinder is operated to open.With this arrangement, the taking and introducing process of part ofcombustion (expansion) gas from one cylinder into another cylinder inthe suction stroke or the compression stroke, can be performed when theion current is high, or the internal pressure of the cylinder is high,or the combustion temperature is high and a large amount of radicals arecontained. Therefore, it is possible to more reliably improve thecombustion characteristics of gas mixture in a cylinder by utilizingradicals generated in another cylinder during the combustion of fuel-airmixture.

[0026] According to a fifth aspect of the present invention, theindividual communication path for each of the cylinders has an openingto the combustion chamber, the opening comprising a swirl port forcausing the combustion (expansion) gas entering through the opening toflow in a swirling manner circumferentially of the cylinder. With thisarrangement, the combustion (expansion) gas introduced in each cylindercan be dispersed uniformly in the entire gas mixture in the cylinder,and further improvement of the combustion characteristics of gas mixturecan be expected.

[0027] According to a sixth aspect of the present invention, theindividual communication path for each of the cylinders is provided witha plurality of openings to the combustion chamber. With thisarrangement, the combustion (expansion) gas can be introduced into eachcylinder through the plurality of openings so that the combustion(expansion) gas can be dispersed uniformly in the entire gas mixture inthe cylinder. Accordingly, further improvement of the combustioncharacteristics of the gas mixture can be expected.

[0028] According to a seventh aspect of the present invention, each ofthe cylinders is provided with a fuel injection valve for injecting fuelinto a cylinder bore of the cylinder. The fuel and air supplied by thefuel injection valve can be greatly activated by the radicals containedin the combustion (expansion) gas introduced in the cylinder, so thatthe combustion characteristics can be further improved.

[0029] According to an eighth aspect of the present invention, thecommon communication path is provided in a cylinder head. With thisarrangement, the common communication path can be kept at a highertemperature, which prevents a temperature drop of the combustion(expansion) gas reliably.

[0030] According to a ninth aspect of the present invention, theopen/close valve of the individual communication path for each cylindercomprises a poppet valve. With this arrangement, the valve can endurethe high pressure in the cylinder, and can be reliably opened or closed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a plan view illustrating a three-cylinder internalcombustion engine according to a first embodiment of the presentinvention.

[0032]FIG. 2 is a vertical section taken along lines II-II in FIG. 1 andviewed from the front side.

[0033]FIG. 3 illustrates strokes in each cylinder of the three-cylinderinternal combustion engine.

[0034]FIG. 4 is an enlarged vertical section, as viewed from the frontside, illustrating a principal portion of a second embodiment.

[0035]FIG. 5 is a plan view illustrating a four-cylinder internalcombustion engine according to a third embodiment of the presentinvention.

[0036]FIG. 6 illustrates strokes in each cylinder of the four-cylinderinternal combustion engine.

[0037]FIG. 7 is a plan view illustrating a six-cylinder internalcombustion engine according to a fourth embodiment of the presentinvention.

[0038]FIG. 8 illustrates strokes in each cylinder of the six-cylinderinternal combustion engine.

[0039]FIG. 9 illustrates the relationship between the crank angle andthe cylinder pressure or the combustion temperature in a three-cylinderinternal combustion engine, the revolution per minute being 2000.

[0040]FIG. 10 illustrates the relationship between the crank angle andthe cylinder pressure or the combustion temperature in thethree-cylinder internal combustion engine, the revolution per minutebeing 4000.

[0041]FIG. 11 illustrates the relationship between the crank angle andthe cylinder pressure or the combustion temperature in a three-cylinderinternal combustion engine, the revolution per minute being 6000.

BEST MODE FOR CARRYING OUT THE INVENTION

[0042] Preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings.

[0043] FIGS. 1-3 illustrate a first embodiment of the present inventionapplied to a conventional in-line three-cylinder four-stroke internalcombustion engine.

[0044] The three-cylinder internal-combustion engine 1 comprises acylinder block 2, a cylinder head 3 secured to an upper surface of thecylinder block. A first cylinder A1, a second cylinder A2 and a thirdcylinder A3, which share a non-illustrated single crank shaft, arearranged in a row extending along a crank axis 4.

[0045] Each of the three cylinders A1, A2 and A3 is provided with acylinder bore 5 provided in the cylinder block 2, a piston 6 which movesreciprocally in the cylinder bore 5, a combustion chamber 7 provided asa recess at a lower surface of the cylinder head 3 to open to thecylinder bore 5, a spark plug 8 attached to the cylinder head 3 to facea generally central portion of the combustion chamber 7, two intakeports 9 provided at the cylinder head 3 for opening to the combustionchamber 7, and two exhaust ports 10 provided at the cylinder head 3 foropening to the combustion chamber 7.

[0046] Each of the cylinders A1, A2 and A3 is further provided with apoppet intake valve 11 for opening and closing the opening of the intakeport 9 to the combustion chamber 7 by an intake valve cam shaft (notshown) which rotates in accordance with the crank shaft, and providedwith a poppet exhaust valve 12 for opening and closing the opening ofthe exhaust port 10 to the combustion chamber 7 by an exhaust valve camshaft (not shown) which rotates in accordance with the crank shaft.

[0047] Each of the cylinders A1, A2 and A3 is further provided with afuel injection valve 13 arranged between the two intake ports 9 forinjecting fuel into the cylinder bore 5 to spread conically with anappropriate angle e in the suction stroke in which the piston 5 movesdownward.

[0048] In this embodiment, ignition for the cylinders A1, A2 and A3 isperformed in the order of the first cylinder A1, the second cylinder A2,and then the third cylinder A3, as is clear from the stroke chart shownin FIG. 3.

[0049] The cylinder head 3 is provided with a common communication path14 which is common to the cylinders A1, A2 and A3 and which extends inthe direction of the row of the cylinders. The common communication path14 is connected to the combustion chamber of each cylinder A1, A2, A3via a communication path 15 provided for each cylinder. Eachcommunication path 15 has an opening to the combustion chamber 7 of thecylinder A1, A2 or A3, which comprises a swirl port extendingtangentially to the cylinder bore 5 in plan view (FIG. 1). The openingis provided with a poppet open/close valve 16 for opening and closingthe opening. The open/close valves of the cylinders A1, A2 and A3 areopened at the same time and remain open for a predetermined period oftime at an earlier stage during the explosion (expansion) stroke and ata later stage during the suction stroke. The operation of the valves 16is performed by utilizing the exhaust valve cam shaft (not shown) foropening and closing the exhaust valve 12 in accordance with the rotationangle (crank angle) of the crank shaft.

[0050] With this arrangement, the open/close valve 16 of the firstcylinder A1 opens for a predetermined time period at an earlier stage inthe explosion (expansion) stroke of the first cylinder A1. At the sametime, the open/close valve 16 of the second cylinder A2 in the suctionstroke, opens for the predetermined time period. As a result, part ofcombustion (expansion) gas in the first cylinder A1 is introduced intothe second cylinder A2 through the common communication path 14.

[0051] Then, the open/close valve 16 of the second cylinder A2 opens fora predetermined time period at an earlier stage in the explosion(expansion) stroke of the second cylinder A2. At the same time, theopen/close valve 16 of the third cylinder A3 in the suction stroke,opens for the predetermined time period. As a result, part of combustion(expansion) gas in the second cylinder A2 is introduced into the thirdcylinder A3 through the common communication path 14.

[0052] Then, the open/close valve 16 of the third cylinder A3 opens fora predetermined time period at an earlier stage in the explosion(expansion) stroke of the third cylinder A3. At the same time, theopen/close valve 16 of the first cylinder A1 in the suction stroke,opens for the predetermined time period. As a result, part of combustion(expansion) gas in the third cylinder A3 is introduced into the firstcylinder A1 through the common communication path 14.

[0053] In this way, part of combustion (expansion) gas in one of thethree cylinders A1, A2 and A3 can be taken out and introduced intoanother one of the remaining cylinders which is in a suction stroke or acompression stroke through the single common communication path 14. Thetaking out of combustion (expansion) gas is performed at an earlierstage in the explosion (expansion) stroke of each cylinder. Further, thecommon communication path 14 is kept at a high temperature, becausecombustion (expansion) gas flows through the path successively from thefirst cylinder A1 to the second cylinder A2, from the second cylinder A2to the third cylinder A3 and from the third cylinder A3 to the firstcylinder A1 at short time intervals. Therefore, combustion (expansion)gas taken out from each cylinder A1, A2, A3 has a high temperature andcan pass through the communication path 14 without largely decreasingits temperature, so that the gas can be introduced into anothercylinder, which is in a suction stroke or a compression stroke, the gaskeeping the high temperature and hence keeping the high content ofradicals.

[0054] As will be understood from FIGS. 9, 10 and 11, it is preferablethat each open/close valve 16 opens at an earlier stage during thecombustion (expansion) stroke of the cylinder, in particular when thecombustion temperature is no less than 1500K. In the cases shown inFIGS. 9, 10 and 11, the open/close valve should be opened before theexhaust valve 12 opens at a crank angle of about 120 degrees.

[0055] The opening of the communication path 15 of each cylinder A1, A2,A3 to the combustion chamber 7 comprises a swirl port which provides thecombustion (expansion) gas entering through the opening with swirlingflow along the circumference of the cylinder bore 5, as indicated by anarrow B. Therefore, the combustion (expansion) gas introduced into eachcylinder A1, A2, A3 can be dispersed generally uniformly in the entiregas mixture in the cylinder.

[0056] Such uniform dispersion of the introduced combustion (expansion)gas in the entire gas mixture in the cylinder can be realized also byproviding the communication path 15 of each cylinder with a plurality ofopenings, each of which may comprise a swirl port.

[0057] In each of the cylinders A1, A2 and A3, air and fuel suppliedinto the cylinder bore 5 by the fuel injection valve 13 during thesuction stroke can be activated by the radicals contained in thecombustion (expansion) gas introduced into the cylinder.

[0058] Instead of injecting fuel into the cylinder bore 5 during thesuction stroke (homogeneous combustion) as in the above-describedinternal fuel injection system, the fuel may be injected into a cavityformed in the top surface of the piston 6 coming close to the top deadcenter at the end of the compression stroke (stratified charge).

[0059] In the above-described embodiment, the open/close valve 16 ofeach cylinder A1, A2, A3 is opened by the rotation of the crankshaft.Instead, however, electrical opening/closing means such as a magneticcoil 17 as shown in FIG. 2 may be provided for causing the open/closevalve to open for a predetermined time period at a predetermined crankangle, i.e. at an earlier stage in the explosion (expansion) stroke andin the suction stroke of the cylinder.

[0060] In the case where the open/close valve 16 is opened by suchelectrical opening/closing means as the magnetic coil 17, each of thecylinders A1, A2 and A3 may be provided with ion current detector fordetecting ion current in the combustion (expansion) gas during theexplosion (expansion) stroke. Based on detection signals from the ioncurrent detector, the open/close valves 16 of one cylinder in which theion current is high is opened so that part of the combustion (expansion)gas of the cylinder is introduced into another cylinder in a suctionstroke or a compression stroke.

[0061] JP-B-S54-27277, for example, discloses ion current detectingmeans utilizing a spark plug. The ion current detecting means 18 asdisclosed in JP-B-S54-27277 maybe applied to the spark plug 8 of eachcylinder A1, A2, A3. The detection signals from the ion currentdetecting means 18 are inputted into electrical opening/closing means,such as a magnetic coil 17, for each open/close valve 16. When the ioncurrent in the cylinder A1, A2, A3 exceeds a predetermined value duringthe explosion (expansion) stroke, the open/close valve 16 is opened.

[0062] As described before, ion current generated by combustion of gasmixture is generally proportional to the pressure in the cylinder duringcombustion, and the pressure in the cylinder during combustion isgenerally proportional to combustion temperature of the gas mixture.Therefore, by causing the open/close valve 16 of each cylinder A1, A2,A3 to open when the ion current exceeds a predetermined value in theexplosion (expansion) stroke, the introduction of part of combustion(expansion) gas from one cylinder into another cylinder in the suctionstroke or the compression stroke can be performed only when the ioncurrent value is high, or the internal pressure of the cylinder is highand hence the combustion temperature is high, and namely, when a largeamount of radicals are contained in the combustion gas.

[0063] In a second embodiment, unlike the compression ratio of 9-10 inan ordinary four-stroke internal combustion engine burning gasoline, thecompression ratio in each-cylinder A1, A2, A3 is set to such a highvalue of about 15-18 as may lead to abnormal combustion such as knockingduring high-load operation. Further, the open/close valves 16 of thecylinders A1, A2 and A3 are operated by the electrical opening/closingmeans such as a magnetic coil 17 which in turn is controlled by acontrol circuit 21 into which signals from a load sensor 19 and a crankangle sensor 20 are inputted in accordance with e.g. the open degree ofa throttle valve. With this arrangement, the cylinder valves, in ahigh-load operation mode, are opened at an earlier stage of theexplosion (expansion) stroke of the cylinders A1, A2, A3 and at a laterstage of the suction stroke, the opening of the valves being implementedat the same crank angle and at the same time, and continued for apredetermined period of time.

[0064] In the above scheme, the open/close valve 16 of each cylinder A1,A2, A3 is not opened in a low-load operation mode nor intermediate-loadoperation mode of the internal combustion engine 1.

[0065] During the high-load operation of the internal combustion engine1, the open/close valve 16 of the first cylinder A1 opens at an earlierstage in the explosion (expansion) stroke of the first cylinder A1 for apredetermined time period. At the same time, the open/close valve 16 ofthe second cylinder A2 in the suction stroke opens for the predeterminedtime period. As a result, part of combustion (expansion) gas in thefirst cylinder A1 is introduced into the second cylinder A2 through thecommon communication path 14.

[0066] Then, the open/close valve 16 of the second cylinder A2 opens atan earlier stage in the explosion (expansion) stroke of the secondcylinder A2 for a predetermined time period. At the same time, theopen/close valve 16 of the third cylinder A3 in the suction stroke opensfor the predetermined time period. As a result, part of combustion(expansion) gas in the second cylinder A2 is introduced into the thirdcylinder A3 through the common communication path 14.

[0067] Then, the open/close valve 16 of the third cylinder A3 opens atan earlier stage in the explosion (expansion) stroke of the thirdcylinder A3 for a predetermined time period. At the same time, theopen/close valve 16 of the first cylinder A1 in the suction stroke opensfor the predetermined time period. As a result, part of combustion(expansion) gas in the third cylinder A3 is introduced into the firstcylinder A1 through the common communication path 14.

[0068] In this way, part of combustion (expansion) gas in one of thethree cylinders A1, A2 and A3 can be taken out and introduced intoanother one of the remaining cylinders, which is in a suction stroke,through the single common communication path 14. Thus, during thehigh-load operation, the combustion pressure in the cylinder is reduced,which contributes to the prevention of abnormal combustion such asknocking, while the combustion characteristics in the cylinder isimproved, which contributes to the increase in output power.

[0069]FIGS. 5 and 6 illustrate a third embodiment of the presentinvention applied to a conventional four-stroke, four-cylinder internalcombustion engine.

[0070] The four-cylinder internal combustion engine 1′ comprises a firstcylinder A1′, a second cylinder A2′, a third cylinder A3′ and a fourthcylinder A4′ which share a non-illustrated single crank shaft and whichare arranged in a row extending along a crank axis 4′.

[0071] As in the first embodiment each of the cylinders A1′, A2′ A3′ andA4′ is provided with a cylinder bore, a piston, a combustion chamber, aspark plug, intake ports with intake valves, exhaust ports with exhaustvalves, a fuel injection valve.

[0072] As seen from the stroke chart shown in FIG. 6, ignition for thecylinders A1′, A2′, A3′ and A4′ of the four-cylinder internal combustionengine 1′ is performed in the order of the first cylinder A1′, the thirdcylinder A3′, the fourth cylinder A4′, and then the second cylinder A2′.

[0073] A single common communication path 14′ is provided which iscommon to the cylinders A1′, A2′, A3′ and A4′ and which extends alongthe row of the cylinders. The common communication path 14′ is connectedto the combustion chamber of each cylinder A1′, A2′, A3′, A4′ via acommunication path 15′ provided for each cylinder. Similarly to thefirst embodiment, the open/close valves 16′ provided at respectivecommunication paths 15′ are designed so that they open at the same timeand for a predetermined period of time at an earlier stage of theexplosion (expansion) stroke and at a later stage of the suction strokein accordance with the rotation of the crank shaft. With the abovearrangement, the open/close valve 16′ of the first cylinder A1′ opens atan earlier stage in the explosion (expansion) stroke of the firstcylinder A1′ for a predetermined time period. At the same time, theopen/close valve 16′ of the third cylinder A3′ in the compression strokeopens for the predetermined time period. As a result, part of combustion(expansion) gas in the first cylinder A1′ is introduced into the thirdcylinder A3′ through the common communication path 14′.

[0074] Then, the open/close valve 16′ of the third cylinder A3′ opens atan earlier stage in the explosion (expansion) stroke of the thirdcylinder A3′ for a predetermined time period. At the same time, theopen/close valve 16′ of the fourth cylinder A4′ in the compressionstroke opens for the predetermined time period. As a result, part ofcombustion (expansion) gas in the third cylinder A3′ is introduced intothe fourth cylinder A4′ through the common communication path 14′.

[0075] Then, the open/close valve 16′ of the fourth cylinder A4′ opensat an earlier stage in the explosion (expansion) stroke of the fourthcylinder A4′ for a predetermined time period. At the same time, theopen/close valve 16′ of the second cylinder A2′ in the compressionstroke opens for the predetermined time period. As a result, part ofcombustion (expansion) gas in the fourth cylinder A4′ is introduced intothe second cylinder A2′ through the common communication path 14′.

[0076] Then, the open/close valve 16′ of the second cylinder A2′ opensat an earlier stage in the explosion (expansion) stroke of the secondcylinder A2′ for a predetermined time period. At the same time, theopen/close valve 16′ of the first cylinder A1′ in the compression strokeopens for the predetermined time period. As a result, part of combustion(expansion) gas in the second cylinder A2′ is introduced into the firstcylinder A1′ through the common communication path 14′.

[0077] In the third embodiment again, the open/close valve 16′ of eachcylinder A1′, A2′, A3′, A4′ may be provided with ion current detectingmeans so that the valve can be opened when the detected ion currentexceeds a predetermined value, as in the first embodiment. Further, thecompression ratio in each cylinder is set high, and part of combustion(expansion) gas of one cylinder is introduced into another cylinder inthe high-load operation mode.

[0078]FIGS. 7 and 8 illustrate a fourth embodiment of the presentinvention applied to a conventional in-line four-stroke six-cylinderinternal combustion engine.

[0079] The six-cylinder internal combustion engine 1″ comprises a firstcylinder A1″, a second cylinder A2″, a third cylinder A3″, a fourthcylinder A4″, a fifth cylinder A5″ and a sixth cylinder A6″ which sharea non-illustrated single crank shaft and which are arranged in a rowextending along a crank axis 4″.

[0080] As in the first embodiment, each of the six cylinders is providedwith a cylinder bore, a piston, a combustion chamber, a spark plug,intake ports with intake valves, exhaust ports with exhaust valves, anda fuel injection valve.

[0081] As seen from the stroke chart shown in FIG. 7, ignition in thecylinders A1″, A2″, A3″, A4″, A5″ and A6″ of the six-cylinder internalcombustion engine 1″ is performed in the order of the first cylinderA1″, the fifth cylinder A5″, the third cylinder A3″, the sixth cylinderA6″, the second cylinder A2″ and then the fourth cylinder A4″.

[0082] A first communication path 14 a″ is common to the first cylinderA1″, the second cylinder A2″ and the third cylinder A3″, while a secondcommunication path 14 b″ is common to the fourth cylinder A4″, the fifthcylinder A5″ and the sixth cylinder A6″. These common paths extend alongthe row of the cylinders A1″, A2″, A3″, A4″, A5″ and A6″. Each of thecommunication paths 14 a″ and 14 b″ is connected to combustion chambersof the relevant cylinders via branch communication paths 15″. Eachbranch communication path 15″ is provided with an open/close valve 16″which, as in the first embodiment, is opened for a predetermined periodof time at an earlier stage of the combustion (expansion) stroke and alater stage of the suction stroke of the relevant cylinder in accordancewith the rotation of the crank shaft.

[0083] With the above arrangement, part of the combustion (expansion)gas in the first cylinders A1″ can be taken out at an earlier stage inits explosion (expansion) stroke and introduced into the third cylinderA3″ in a suction stroke through the first communication path 14 a″. Partof the combustion (expansion) gas in the fifth cylinders A5″ can betaken out at an earlier stage in its explosion (expansion) stroke andintroduced into the sixth cylinder A6″ in a suction stroke through thesecond communication path 14 b″. Part of the combustion (expansion) gasin the third cylinders A3″ can be taken out at an earlier stage in itsexplosion (expansion) stroke and introduced into the second cylinder A2″in a suction stroke through the first communication path 14 a″ Part ofthe combustion (expansion) gas in the sixth cylinders A6″ can be takenout at an earlier stage in its explosion (expansion) stroke andintroduced into the fourth cylinder A4″ in a suction stroke through thesecond communication path 14 b″. Part of the combustion (expansion) gasin the second cylinder A2″ can be taken out at an earlier stage in itsexplosion (expansion) stroke and introduced into the first cylinder A1″in a suction stroke through the first communication path 14 a″ Part ofthe combustion (expansion) gas in the fourth cylinder A4″ can be takenout at an earlier stage in its explosion (expansion) stroke andintroduced into the fifth cylinder A5″ in a suction stroke through thesecond communication path 14 b″.

[0084] In the fourth embodiment again, the open/close valve 16″ of eachof the six cylinders A1″, A2″, A3″, A4″, A5″ and A6″ may be providedwith ion current detecting means, as in the first embodiment, so thatthe valve is opened when the detected ion current exceeds apredetermined value. Further, the compression ratio in each cylinder isset high, and part of combustion (expansion) gas of one cylinder isintroduced into another cylinder in the high-load operation mode.

[0085] The present invention is applicable to a V-type six-cylinder oreight-cylinder internal combustion engine, in which case a communicationpath common to three or four cylinders is provided for each cylinderblock.

[0086] Further, the present invention is not limited to a four-strokemulticylinder internal combustion engine burning gasoline, butapplicable to a two-stroke multicylinder internal combustion engine or acompression-ignition type multicylinder internal combustion engine suchas a diesel engine.

1. A multicylinder internal combustion engine provided with a pluralityof cylinders sharing a single crankshaft, the engine comprisingarrangement for the respective cylinders, whereby part of combustion(expansion) gas is taken out from one of the cylinders at an earlierstage of an explosion (expansion) stroke, and introduced into anothercylinder of the remaining cylinders in a suction stroke or compressionstroke through a communication path.
 2. A multicylinder internalcombustion engine provided with a plurality of cylinders sharing asingle crankshaft, wherein a compression ratio in each of the cylindersis set to such a high value as would lead to abnormal combustion such asknocking during high-load operation, the engine further comprisingarrangement for the respective cylinders during the high-load operation,whereby part of combustion (expansion) gas is taken out from one of thecylinders at an earlier stage of an explosion (expansion) stroke, andintroduced into another cylinder of the remaining cylinders in a suctionstroke or compression stroke through a communication path.
 3. Amulticylinder internal combustion engine provided with a plurality ofcylinders sharing a single crankshaft, the engine comprising a singlecommon communication path extending along a row of the cylinders,wherein the common communication path is connected to combustionchambers of the respective cylinders via individual communication pathsprovided for the cylinders, the individual communication paths of thecylinders being provided with open/close valves, the valves being openedat an earlier stage of an explosion (expansion) stroke of the relevantcylinders so that part of combustion (expansion) gas produced in one ofthe cylinders is introduced into another one of the cylinders in asuction or compression stroke.
 4. The multicylinder internal combustionengine according to claim 3, wherein each cylinder is provided with anion current detector for detecting ion current in combustion (expansion)gas during the explosion (expansion) stroke of the cylinder so that theopen/close valve of the cylinder opens when the ion current in one ofthe cylinders is determined to be high based on a detection signal fromthe ion current detector.
 5. The multicylinder internal combustionengine according to any one of claims 1 through 4, wherein theindividual communication path for each of the cylinders has an openingto the combustion chamber, the opening comprising a swirl port forcausing the combustion (expansion) gas entering through the opening toflow in a swirling manner circumferentially of the cylinder.
 6. Themulticylinder internal combustion engine according to any one of claims1 through 5, wherein the individual communication path for each of thecylinders is provided with a plurality of openings to the combustionchamber.
 7. The multicylinder internal combustion engine according toany one of claims 1 through 6, wherein each of the cylinders is providedwith a fuel injection valve for injecting fuel into a cylinder bore ofthe cylinder.
 8. The multicylinder internal combustion engine accordingto any one of claims 3 through 7, wherein the common communication pathis provided in a cylinder head.
 9. The multicylinder internal combustionengine according to any one of claims 3 through 8, wherein theopen/close valve of the individual communication path for each cylindercomprises a poppet valve.